Multi-Band OFDM Communications System

ABSTRACT

A method for providing communication in a wireless network comprising one or more simultaneously operating pico networks includes dividing UWB spectrum into a plurality of frequency bands. These bands are formed into band groups. At least one band group is assigned to each one of the pico networks. At least pne time frequency code is assigned to symbols associated with each one of the pico networks on a transmission-by-transmission basis. A system for channelization of the spectrum includes a frequency-synthesized oscillator and a time frequency code generator configured to assign time-frequency codes to successive transmissions of a pico network such that the successive transmissions are transmitted in all frequency bands of a band group assigned to the pico network.

This application is a Divisional of claims priority under 35 U.S.C. §120to U.S. patent application Ser. No. 10/844,832, filed May 13, 2004 whichclaims the benefit of U.S. Provisional Applications: No. 60/470,532,filed May 14, 2003, entitled “Interleaving Sequences for MultipleAccess;” and No. 60/477,184, filed Jun. 10, 2003, entitled “6-ChannelOption for a TFI-OFDM System;” which applications are herebyincorporated herein by reference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the following co-pending and commonlyassigned patent application Ser. No. 10/688,169, filed Oct. 18, 2003,entitled “Time-Frequency Interleaved Orthogonal Frequency DivisionMultiplexing Ultra Wide Band Physical Layer,” which application isincorporated by reference.

TECHNICAL FIELD

The present invention relates generally to a system and method fordigital communications, and more particularly to a system and method forproviding multiple access in a multi-band, orthogonal frequency divisionmultiplexed (multi-band-OFDM) digital communications system.

BACKGROUND

In order for a communications device to successfully complete atransmission, a collision should not occur with transmissions from othercommunications devices or with noise and other types of interference. Itmay be possible to recover from a collision with another transmission(or noise or other types interference) via the use of error detectingand correcting codes. However, such recovery is normally possible onlyif a small percentage of the transmission contains unreliable bits orinformation, such as a result of transient noise or interference, andnot when a large percentage of the transmission is damaged, which isnormally the case when a collision with another transmission occurs.Furthermore, the use of error detecting and correcting codes that canrecover from significant damage can greatly reduce the overallthroughput performance of a communications system due to the codingoverhead.

One way to help reduce the probability of transmission collisions is todivide the available bandwidth in the communications channel intomultiple transmission bands and then assign certain communicationsdevices to the various transmission bands, wherein the communicationsdevices can only transmit within their assigned transmission bands. Byassigning communications devices to different transmission bands, theprobability of collisions with other transmissions can be reduced. Ifthe number of transmission bands is equal to or greater than the numberof communications devices, then the probability of collisions can bereduced to zero.

Another way to help reduce the probability of transmission collisions isto allocate access to the communications channel based upon time,wherein a communications device can transmit only if it is within itstransmission time window. Once again, the probability of collisions canbe reduced to zero if only one communications device is assigned to atransmission time window.

One disadvantage of the prior art is that if the available bandwidth isdivided into a large number of transmission bands, then the total amountof bandwidth available to a single communications device can be a smallfraction of the total bandwidth. If only a small number ofcommunications devices are transmitting, then the bandwidth utilizationcan be small, resulting in the waste of a significant amount of theavailable bandwidth.

A second disadvantage of the prior art is that unless properlyallocated, the transmission time windows can be allocated tocommunications devices with nothing to transmit, while communicationsdevices with a need to transmit may not receive enough transmission timewindows to achieve adequate data throughput. Once again, this can leadto inefficient use of the available transmission bandwidth.

Another disadvantage of the prior art is that should an adaptivetechnique be applied to either the transmission bands or thetransmission time windows, to increase bandwidth utilization, forexample, then considerable resources may be needed to fairly andeffectively distribute available bandwidth. This may require the use ofa dedicated bandwidth server (or processor), which can increase thecosts of the communications system.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by preferred embodiments ofthe present invention which provides for a multi-channel transmitfrequency interleaved, orthogonal frequency division multiplexedcommunications system and multiple access sequences for thecommunications system.

In accordance with a preferred embodiment of the present invention, amethod for receiving a preamble includes receiving a current preamblethat can be used for channel estimation. The current preamble is usedfor the estimation of channels present in both enhanced and legacytime-interleaved, orthogonal frequency division multiplexedcommunications systems. A header that contains physical layer parametersand media access control layer information is received. Also received isa channel estimation extension used for channel estimation. The channelestimated by the channel estimation extension are only present in theenhanced time-frequency interleaved, orthogonal frequency divisionmultiplexed communications system. Other embodiments of the inventionprovide other features.

An advantage of a preferred embodiment of the present invention is thatthe multiple access communications system can accommodate known sourcesof interferers and frequency bands that should be avoided, to mitigateinterference from and to these known trouble spots.

A further advantage of a preferred embodiment of the present inventionis that transmission collisions in the communications system can bereduced with little or no scheduling or processing overhead. Therefore,a dedicated bandwidth scheduler or processor may not be needed, hencepotentially reducing the cost of the communications system.

Yet another advantage of a preferred embodiment of the present inventionis that a reduction in transmission collisions can improve thetransmission throughput of the communications system, as well as theoverall robustness of the communications system since it may not need tosignificantly degrade throughput to recover from collisions.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1 a and 1 b are coverage maps of multiple piconets operatingwithin close proximity of one another;

FIG. 2 is a diagram of a frequency allocation for a wirelesscommunications system;

FIGS. 3 a and 3 b are diagrams of time-frequency interleaving sequencesof length three and six, according to a preferred embodiment of thepresent invention;

FIGS. 4 a through 4 c are diagrams of possible transmission collisionsbetween transmission sequences, according to a preferred embodiment ofthe present invention;

FIG. 5 is a diagram of a frequency allocation for a wirelesscommunications system, wherein a portion of the frequency is occupied bya known interferer, according to a preferred embodiment of the presentinvention;

FIG. 6 is a diagram of a transmission sequence in an enhancedmulti-band-OFDM wireless communications system with additionaltransmissions bands containing an enhanced preamble to support theadditional transmission bands, according to a preferred embodiment ofthe present invention;

FIG. 7 is a diagram of a transmission sequence in an enhancedmulti-band-OFDM wireless communications system with additionaltransmissions bands containing an enhanced preamble to support theadditional transmission bands, according to a preferred embodiment ofthe present invention;

FIG. 8 is a diagram of time-frequency interleaving sequences of lengthsix for a communications system with six transmission bands, accordingto a preferred embodiment of the present invention;

FIGS. 9 a and 9 b are diagrams of time-frequency interleaving sequencesof length six for a communications system using three transmissionbands, according to a preferred embodiment of the present invention;

FIG. 10 is a diagram of a frequency allocation chart for amulti-band-OFDM wireless communications system, according to a preferredembodiment of the present invention;

FIG. 11 is a diagram of a frequency allocation chart for amulti-band-OFDM wireless communications system, wherein sets of twotransmission bands have been bonded into one transmission band,according to a preferred embodiment of the present invention;

FIG. 12 is a diagram of a frequency allocation chart for amulti-band-OFDM wireless communications system, wherein sets of threetransmission bands have been bonded into one transmission band,according to a preferred embodiment of the present invention;

FIG. 13 is a diagram of a frequency allocation chart for amulti-band-OFDM wireless communications system, wherein sometransmission bands have been bonded and some have not been bonded,according to a preferred embodiment of the present invention;

FIG. 14 is a flow diagram of an algorithm for use in configuringtransmission bands for a multi-band-OFDM wireless communications system,according to a preferred embodiment of the present invention;

FIG. 15 is a flow diagram of an algorithm for use in bondingtransmission bands for a multi-band-OFDM wireless communications system,according to a preferred embodiment of the present invention; and

FIG. 16 is a diagram of a wireless communications system containing bothlegacy and enhanced communications devices, according to a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferredembodiments in a specific context, namely a multi-band, orthogonalfrequency division multiplexed (multi-band-OFDM) wireless communicationssystem, such as one that is adherent to IEEE 802.15.3a technicalspecifications. The IEEE 802.15.3a technical requirements can be foundin a document entitled “TG3a Technical Requirements,” published Dec. 27,2002, which is herein incorporated by reference. The invention may alsobe applied, however, to other communications systems, namely those thatmake use of a partitioning of available bandwidth into transmissionbands and those that operate in areas with known sources of interferenceand frequency bands that need to be avoided.

The IEEE 802.15.3a technical requirements has specified a set ofperformance criteria, such as bit rate, effective operating range, powerconsumption, and so forth, for wireless devices. For example, a bit rateof at least 110 Mb/s at 10 meters is required. The technicalrequirements also specify that the communications system must be able tocoexist with other wireless devices that may be in close proximity.

With reference now to FIGS. 1 a and 1 b, there are shown diagramsillustrating a coverage map (100 (FIG. 1 a) and 150 (FIG. 1 b)) ofmultiple piconets operating within close proximity of one another. Thecoverage map 100 illustrates three piconets (piconet A 105, piconet B110, and piconet C 115) operating in close proximity, so close thatportions of their coverage areas overlap. The coverage map 150illustrates four piconets (piconets A through C and piconet D 155),wherein the piconets' coverage areas overlap.

Within the areas where the piconets' coverage areas overlap,transmissions from a transmitter in one piconet can collide withtransmissions from a transmitter in another piconet. For example, atransmitter (not shown) in piconet A 105 may have its transmissionscollide with transmissions from a transmitter (not shown) in piconet C115.

With reference now to FIG. 2, there is shown a diagram illustrating afrequency allocation 200 for a wireless communications system. Asdiscussed previously, one way to help decrease the probability oftransmission collisions is to divide the available bandwidth intomultiple transmission bands and then assign certain transmitters totransmit within certain transmission bands. As shown in FIG. 2, thefrequency allocation 200 is for a wireless communications system thatoperates within a frequency band of 3.168 GHz to 4.752 GHz, wherein thefrequency band has been divided into three transmission bands: a firsttransmission band 205 with a center frequency at 3.432 GHz, a secondtransmission band 210 with a center frequency at 3.960 GHz, and a thirdtransmission band 215 with a center frequency at 4.488 GHz. With threetransmission bands, the wireless communications system may be able tosupport three piconets, which can be simultaneously transmitting,without collision. If more than three piconets are to be supported, thenthere may be transmission collisions, since there will be at least onetransmission band wherein more than one piconet that may betransmitting.

However, rather than assigning a piconet to transmit only within acertain transmission band, which can result in a waste of bandwidthallocated to the transmission band if the piconet is not transmitting,it may be possible to specify an order of usage of the transmissionbands that can be used by a piconet. The order of usage, which may bereferred to as a transmission sequence, can specify a sequence oftransmission bands that the piconet should use when transmitting. Forexample, if the piconet transmits during a certain time interval, thenit should use a transmission band specified for use during that timeinterval, and if it has something to transmit during the subsequentinterval, then it should use a transmission band specified for thesubsequent interval. When properly specified, the use of thetransmission sequence can result in a relatively low probability oftransmission collisions combined with usage of the entire bandwidth ofthe communications system.

With reference now to FIGS. 3 a and 3 b, there are shown diagramsillustrating time-frequency interleaving sequences (TFIS) of lengththree (FIG. 3 a) and six (FIG. 3 b) for a multi-band OFDM wirelesscommunications system with three transmission bands, according to apreferred embodiment of the present invention. For discussion purposes,let the three transmission bands be referred to by their numericalidentifiers: “1,” “2,” and “3.” Then, for transmission sequences oflength three, there may be two transmission sequences that can be shownto be optimal. A first transmission sequence 305 can be specified as [12 3] and a second transmission sequence 310 can be specified as [1 3 2].Note that when using time-interleaving, a multi-band OFDM wirelesscommunications system may be referred to as a TFI-OFDM wirelesscommunications system.

The first transmission sequence 305 and the second transmission sequence310 are considered to be optimal because if they are used to specifytransmissions for two asynchronous piconets with overlapping coverageareas, then there may be a guarantee of only a single collision over anythree transmissions. For example, if piconet A transmits using the firsttransmission sequence 305 and piconet B transmits using the secondtransmission sequence 310 and both start transmissions at the same time,then only their initial transmissions will collide, with the twosubsequent transmissions being carried on different transmission bandsand hence no collisions will occur.

FIG. 3 b illustrates four transmission sequences of length six. Thesefour length six sequences (a first sequence 355, a second sequence 360,a third sequence 365, and a fourth sequence 370) can be used to permitup to four asynchronous piconets with overlapping coverage areas sharethree transmission bands. Note that the four length six sequences arewhat can be considered near-optimal. They are near-optimal in thatcertain pairs of the sequences are pairwise optimal, but not every pairof the sequences are pairwise optimal. One way to find transmissionsequences is via simulation.

With reference now to FIGS. 4 a through 4 c, there are shown diagramsillustrating possible transmission collisions between two transmissionsequences, according to a preferred embodiment of the present invention.FIG. 4 a displays two transmission sequences: the first transmissionsequence 305 being [1 2 3] and the second transmission sequence 310being [1 3 2] as shown in FIG. 3 a. If two asynchronous piconets were touse the two transmission sequences as shown, then a transmissioncollision 405 may occur during a first specified transmission time whenboth asynchronous piconets transmit on transmission band #1. Note thatthe subsequent transmission times may not result in transmissioncollisions since different transmission bands are being used.

With reference now to FIG. 4 b, which displays two transmissionsequences, the first transmission sequence 305 and a shifted version 410of the second transmission sequence 305. The shifted version 410 mayrepresent a transmission sequence used by an asynchronous piconet with adifferent transmission time clock. If two asynchronous piconets were touse the two transmission sequences as shown, then a transmissioncollision 415 may occur during a third specified transmission time whenboth asynchronous piconets transmit on transmission band #3.

With reference now to FIG. 4 c, which displays two transmissionsequences, the first transmission sequence 305 and a shifted version 420of the second transmission sequence 305. The shifted version 420 mayrepresent a transmission sequence used by an asynchronous piconet with adifferent transmission time clock. If two asynchronous piconets were touse the two transmission sequences as shown, then a transmissioncollision 425 may occur during a second specified transmission time whenboth asynchronous piconets transmit on transmission band #2. A similarset of diagrams can be used to show potential transmission collisionsfor the length six sequences (the first sequence 355, the secondsequence 360, the third sequence 365, and the fourth sequence 370)displayed in FIG. 3 b.

The partitioning of available transmission bandwidth into a plurality oftransmission bands has been shown to enable the sharing of thetransmission bandwidth by multiple asynchronous (uncoordinated)piconets. In addition to the simple sharing of the available bandwidthamong multiple piconets, the transmission bands can also be used toavoid interference from other electronic devices and noise andinterfering with other electronic devices. Avoiding interference fromand interfering with other electronic devices may be accomplished by notusing (and listening to) transmission bands that occupy the samefrequency bands as those used by the electronic devices as long as theseelectronic devices (and their frequency bands) are known before hand.

With reference now to FIG. 5, there is shown a diagram illustrating afrequency allocation 500 for a wireless communications system, wherein aportion of the frequency is occupied by a known interferer, according toa preferred embodiment of the present invention. As specified by theIEEE 802.15.3a technical requirements, a communications system that iscompliant must be able to accept interference from and not cause undointerference to other electronic devices operating nearby. A frequencyband that is seeing a great deal of interest is the Unified NationalInformation Infrastructure (UNII) band, located at 5.15 to 5.825 GHz.The UNII band has been used for wireless computer networking, cordlesstelephones, and other unlicensed devices in countries such as the UnitedStates and Japan.

One way to not cause interference to and receive interference fromelectronic devices operating at a frequency range may be to exclude thefrequency range from any transmissions. By preventing transmissions fromusing the excluded frequency range (such as the UNII band), electronicdevices operating in the excluded frequency range will not be interferedwith and the communications system will not receive interference fromthe electronic devices since the communications system will not beexpecting transmissions from the excluded frequency range.

FIG. 5 displays the frequency allocation 500 for a communicationssystem, wherein the frequency allocation 500 features six transmissionbands: the first transmission band 205 with a center frequency at 3.432GHz, the second transmission band 210 with a center frequency at 3.960GHz, the third transmission band 215 with a center frequency at 4.488GHz, a fourth transmission band 510 with a center frequency at 6.336GHz, a fifth transmission band 515 with a center frequency at 6.864 GHz,and a sixth transmission band 520 with a center frequency at 7.392 GHz.Note that the first, second, and third transmission bands (205, 210, and215) may be similar to the transmission bands displayed in the frequencyallocation 200 (FIG. 2).

The first, second, and third transmission bands (205, 210, and 215) maybe below a frequency band 505 that can be representative of the UNIIfrequency band, while the fourth, fifth, and sixth transmission bands(510, 515, and 520) may be above the frequency band 505. Note thatdepending upon the actual location of the frequency band 505 and thedesired number of transmission frequencies, the location (centerfrequencies) of transmission bands may be different. For example, theremay be a desire for only four transmission bands or there may bemultiple frequency bands to avoid, both of which can change thefrequency allocation. Furthermore, depending on the number of piconetsto support as well as the amount of spectrum available, it may bepossible to add additional transmission bands or it may not be possibleto have all six transmission bands as shown. The allocation of thespectrum may be dependent upon factors such as the number of piconets tosupport, the presence of known interferers, the amount of spectrumavailable, and so forth.

Note that by simply repeating the frequency allocation 200 of FIG. 2, atotal of 264 MHz of spectrum may be wasted. One way to recover this lostspectrum may be to introduce a frequency offset of 264 MHz to thetransmission bands above the frequency band 505, namely, the fourth,fifth, and sixth transmission bands (510, 515, and 520). Using wellknown single-sideband generation techniques, the center frequencies ofeach of the transmission bands can be generated. Starting with afrequency of 8448 MHz, the continued division by a factor of two (2) canresult in frequencies of 4224 MHz, 2112 MHz, 1056 MHz, 528 MHz, and 264MHz. Note that for a different frequency allocation, a differentstarting frequency and division factor may be needed. Then, using thegenerated frequencies, the center frequencies of the transmission bandscan be generated as follows (note that it can be possible to express thecenter frequencies as a sum (and difference) of powers of two (2)factors of the smallest generated frequency, 264 MHz):

$\begin{matrix}\begin{matrix}{{3432\mspace{14mu} {MHz}} = {{4224\mspace{14mu} {MHz}} - {1056\mspace{14mu} {MHz}} + {264\mspace{14mu} {MHz}}}} \\{= {{16^{*}a} - {4^{*}a} + {a\mspace{20mu} \left( {{{wherein}\mspace{14mu} a} = {264\mspace{14mu} {MHz}}} \right)}}}\end{matrix} & {{Band}{\# 1}} \\{{3960\mspace{14mu} {MHz}} = {{{4224\mspace{14mu} {MHz}} - {264\mspace{14mu} {MHz}}} = {{16^{*}a} - a}}} & {{Band}{\# 2}} \\{{4488\mspace{14mu} {MHz}} = {{{4224\mspace{14mu} {MHz}} + {264\mspace{14mu} {MHz}}} = {{16^{*}a} + a}}} & {{Band}{\# 3}} \\\begin{matrix}{{6336\mspace{14mu} {MHz}} = {{4224\mspace{14mu} {MHz}} + {2112\mspace{14mu} {MHz}}}} \\{= {{8448\mspace{14mu} {MHz}} - {2112\mspace{14mu} {MHz}}}} \\{= {{16^{*}a} + {8^{*}a}}}\end{matrix} & {{Band}{\# 4}} \\\begin{matrix}{{6864\mspace{14mu} {MHz}} = {{4224\mspace{14mu} {MHz}} + {2112\mspace{14mu} {MHz}} + {528\mspace{14mu} {MHz}}}} \\{= {{8448\mspace{14mu} {MHz}} - {528\mspace{14mu} {MHz}}}} \\{= {{16^{*}a} + {8^{*}a} + {2^{*}a}}}\end{matrix} & {{Band}{\# 5}} \\\begin{matrix}{{7392\mspace{14mu} {MHz}} = {{4224\mspace{14mu} {MHz}} + {2112\mspace{14mu} {MHz}} + {1056\mspace{14mu} {MHz}}}} \\{= {{8446\mspace{14mu} {MHz}} - {1056\mspace{14mu} {MHz}}}} \\{= {{16^{*}a} + {8^{*}a} + {4^{*}{a \cdot}}}}\end{matrix} & {{Band}{\# 6}}\end{matrix}$

Since each transmission band's center frequency may be expressed as asum (and/or difference) of powers of two factors of the smallestgenerated frequency, a single circuit may be used to generate the centerfrequency for both the lower three transmission bands (the first,second, and third transmission bands 205, 210, and 215) and the upperthree transmission bands (the fourth, fifth, and sixth transmissionbands 510, 515, and 520). Since a single circuit can be used to generateall of the center frequencies, the generation of the center frequenciescan be simplified and may be more efficient, when compared to techniquesthat may require multiple center frequency generating circuits. Notethat should additional transmission bands (above the sixth transmissionband 520) be desired, the same technique can be used to generate theircenter frequencies.

In a multi-band-OFDM wireless communications system, a preamble sequencecan be used for packet detection, frame synchronization, frequencyoffset estimation, channel estimation, and so forth. Therefore, whenadditional transmission bands are added to a multi-band-OFDM wirelesscommunications system, the preamble sequence should be modified in sucha way that the previous uses of the preamble sequence (such as packetdetection, frame synchronization, frequency offset estimation, andchannel estimation) can be used in the additional transmission bands.However, compatibility with existing multi-band-OFDM wirelesscommunications systems without the additional transmission bands shouldbe maintained. Therefore, the modified preamble sequence should be ableto be used in both existing and enhanced multi-band-OFDM wirelesscommunications systems without modification.

With reference now to FIG. 6, there is shown a space-time diagramillustrating a transmission sequence 600 in an enhanced multi-band-OFDMwireless communications system with additional transmissions bandscontaining an enhanced preamble to support the additional transmissionbands, according to a preferred embodiment of the present invention. Afirst approach to extending a preamble sequence for an enhancedmulti-band-OFDM wireless communications system can be to maintain anexisting preamble sequence 630 and then after the existing preamblesequence 630, adding a channel estimation extension 645, which can beused to estimate the channel response on the additional transmissionbands.

The transmission sequence 600 displays the transmissions for amulti-band-OFDM wireless communications system with six transmissionbands (such as transmission band #1 605, band #2 610, band #4 615, andband #5 620). The transmission sequence 600 displays the existingpreamble 630, which can comprise a current preamble 635 and a PLCPheader 640. Note that the existing preamble 630 can be compatible inmulti-band-OFDM wireless communications systems without the additionaltransmissions bands (i.e., a legacy multi-band-OFDM wirelesscommunications system), therefore, transmissions in the existingpreamble 630 are contained in the existing transmission bands(transmissions bands #1 605, #2 610, and #3). The channel estimationextension 645 can contain transmissions on the additional transmissionbands (transmission bands #4 615, #5 620, and #6) and thesetransmissions can be used to compute estimations of the additionaltransmission bands. A payload 650 contains data and controltransmissions using the various transmission bands.

An advantage of adding the channel estimation extension 645 at the endof the existing preamble 630 may be that existing devices (commonlyreferred to as legacy devices), i.e., devices that only communicationusing transmission bands #1, #2, and #3, can always decode the existingpreamble 630 (the current preamble 635 and the PLOP header 640) and canbe able to configure their network allocation vector (NAV)appropriately. An additional advantage of adding the channel estimationextension 645 at the end of the existing preamble 630 can be that adevice can use the PLOP header 640 to signal the presence of the channelestimation extension 645 and whether or not the payload 650 will beusing the additional transmission channels. This can allow receivers theluxury of not needing to know a priori the transmission mode of thetransmitter.

With reference now to FIG. 7, there is shown a space-time diagramillustrating a transmission sequence 700 for use in an enhancedmulti-band-OFDM wireless communications system with additionaltransmissions bands containing an enhanced preamble to support theadditional transmission bands, according to a preferred embodiment ofthe present invention. A second approach to extending a preamblesequence for an enhanced multi-band-OFDM wireless communications systemcan be to insert a channel estimation extension 705 in between thecurrent preamble 635 and the PLOP header 640. As previously, the channelestimation extension 705 can be used to estimate the channel response onthe additional transmission bands.

The transmission sequence 700 displays the transmissions for amulti-band-OFDM wireless communications system with six transmissionbands (numbered #1 through #6). The transmission sequence 700 displaysthe current preamble 635 and the PLOP header 640 with the channelestimation extension 705 positioned in between the two. An advantage ofinserting the channel estimation extension 705 in between the currentpreamble 635 and the PLOP header 640 can be that it fits more naturallywith the frequency division multiple access (FDMA) technique, i.e., thepreamble (comprising the current preamble 635, the channel estimationextension 705, and the PLCP header 640) can be readily scaled to asingle channel.

With reference now to FIG. 8, there is shown a diagram illustratingtime-frequency interleaving sequences (TFIS) of length six for acommunications system with six transmission bands, according to apreferred embodiment of the present invention. For discussion purposes,let the six transmission bands be referred to by numerical identifiers:“1,” “2,” “3,” “4,” “5,” and “6.” Then, for transmission sequences oflength six, there may be four transmission sequences that can be shownto be near optimal. A first transmission sequence 805 can be specifiedas [1 2 3 4 5 6], a second transmission sequence 810 can be specified as[1 4 6 2 3 5], a third transmission sequence 815 can be specified as [13 2 6 5 4], and a fourth transmission sequence 820 can be specified as[1 4 2 5 6 3]. The four transmission sequences shown in FIG. 8 canpermit the sharing of six transmission bands by four transmitters withnear optimal performance. Note that transmission sequences of differentlength can be specified, some of which may be optimal.

With reference now to FIGS. 9 a and 9 b, there are shown diagramsillustrating time-frequency interleaving sequences of length six for acommunications system using three transmission bands, according to apreferred embodiment of the present invention. In a wirelesscommunications system, a single transmitter may be allowed to transmiton all of the available transmission bands (such as shown in the TFISshown in FIG. 8). However, it may also be possible to limit a singletransmitter to a subset of the available transmission bands. By limitingthe number of transmission bands that a single transmitter can use, thenit can be possible to increase the number of transmitters that can usethe transmission bands. For example, in a wireless communications systemwith six transmission bands, if each transmitter is limited to threetransmission bands, then four transmitters can share each group of threetransmission bands (using the TFIS shown in FIG. 3 b, for example) for atotal of eight transmitters in the wireless communications system.

FIG. 9 a displays two transmission sequences of length six using threetransmission bands, a first transmission sequence 905 can be specifiedas [4 5 6 4 5 6] and a second transmission sequence 910 can be specifiedas [4 6 5 4 6 5]. FIG. 9 b displays two transmission sequences of lengthsix using three transmission bands, wherein the transmission bands aredifferent from those shown in FIG. 9 a. The transmission sequences shownin FIG. 9 b may be a first transmission sequence 955 that can bespecified as [1 2 3 1 2 3] and a second transmission sequence 960 thatcan be specified as [1 3 2 1 3 2].

In a given wireless communications system, each transmission band mayhave a fixed bandwidth. Furthermore, in a multi-band-OFDM wirelesscommunications system, the available bandwidth can be allocated toprovide a desired transmission range, at the expense of data rate.Therefore, for a given application, the bandwidth afforded by atransmitter's allocated transmission band may not be able to provide adesired data rate or transmission range. In a lightly used wirelesscommunications system, it may be possible to increase the data rateand/or transmission range at a cost of reducing the number of availabletransmission bands (and hence reducing the total number of transmittersthat can be supported).

With reference now to FIG. 10, there is shown a diagram illustrating afrequency allocation chart 1000 for a multi-band-OFDM wirelesscommunications system, according to a preferred embodiment of thepresent invention. The frequency allocation chart 1000 may illustrateone possible transmission band allocation for a multi-band-OFDM wirelesscommunications system. As shown, there are 12 transmission bands(numbered from #1 to #12), such as transmission band #1 1007. The 12transmission bands can be partitioned into groups of three, for example,group #1 1005 can be made up of transmission bands #1, #2, and #3, whilegroup #2 1010 can be made up of transmission bands #4, #5, and #6, andso forth.

As discussed previously, the partitioning of the available transmissionbands can permit a greater number of transmitters to share the availablebandwidth. As shown in FIG. 10, each transmission band can have abandwidth of 528 MHz, which when using OFDM with no coding and nospreading, a maximum bit rate of 640 Mbps may be possible. In additionto using multi-band-OFDM, it may be possible to transmit OFDM symbols ina frequency-division multiplexing (FDM) mode, wherein the OFDM symbolsare transmitted on a single transmission band (no time-frequencyinterleaving). An advantage in the use of TFI-OFDM over the FDM-OFDM maybe an increase in range and robustness to multipath. Regardless of theway that the OFDM symbols are transmitted (either TFI-OFDM or FDM-OFDM),the maximum bit rate remains at 640 Mbps. Note that the frequencyallocation chart 1000 displayed in FIG. 10 is but one way to allocatethe available spectrum. Other spectrum allocations may be possible, witha larger (or smaller) number of transmission bands, with a larger (orsmaller) number of transmission bands per group, with (or without)frequency bands set aside for known interferers, and so forth.

As displayed in FIG. 10, there are four groups of three transmissionbands (groups #1, #2, #3, and #4). Referring back to FIG. 3 b, there canbe four optimal time-frequency interleaved sequences of length six foruse with three transmission bands. Therefore, it can be possible for theTFI-OFDM wireless communications system with the frequency allocationchart 1000 to support up to 16 piconets, i.e., four piconets per groupof three transmission bands.

With reference now to FIG. 11, there is shown a diagram illustrating afrequency allocation chart 1100 for a multi-band-OFDM wirelesscommunications system, wherein sets of two transmission bands have beenbonded into one transmission band, according to a preferred embodimentof the present invention. The frequency allocation chart 1100 mayillustrate one possible transmission band allocation for amulti-band-OFDM wireless communications system, wherein singletransmission bands, such as transmission band #1 1107 may be made frombonding two smaller transmission bands. Note that the frequencyallocation chart 1100 may represent a multi-band-OFDM wirelesscommunications system made from a multi-band-OFDM wirelesscommunications system whose frequency allocation may have been shown inFIG. 10.

With each transmission band being made by binding two smallertransmission bands (and using the frequency allocation chart 1000 as adiscussion reference), each transmission band may have a bandwidth of1056 MHz and when using OFDM with no coding and no spreading, a maximumbit rate of 1280 Mbps may be possible. Once again, the transmissionbands may be partitioned into groups of three, such as group #1 1105that can be made up of transmission bands #1, #2, and #3. Note thatsince each transmission band is made up of two smaller transmissionbands, the total number of transmission bands available in themulti-band-OFDM wireless communications system is smaller than the totalnumber of transmission bands available in the multi-band-OFDM wirelesscommunications system shown in FIG. 10. Furthermore, FIG. 11 displaysone possible spectrum allocation and there may be other possiblespectrum allocations.

As discussed above, if a TFI-OFDM wireless communications system withthe frequency allocation chart 1100 makes use of the four time-frequencyinterleaved sequences of length six displayed in FIG. 3 b, then it maybe able to support up to eight piconets, wherein each piconet cantransmit at up to twice the bit rate of piconets using unbondedtransmission bands. Alternatively, the piconets can take advantage ofthe greater bandwidth to achieve greater operating range.

With reference now to FIG. 12, there is shown a diagram illustrating afrequency allocation chart 1200 for a multi-band-OFDM wirelesscommunications system, wherein sets of three transmission bands havebeen bonded into one transmission band, according to a preferredembodiment of the present invention. The frequency allocation chart 1200may illustrate one possible transmission band allocation for amulti-band-OFDM wireless communications system, wherein singletransmission bands, such as transmission band #1 1207 may be made frombonding three smaller transmission bands. Note that the frequencyallocation chart 1200 may represent a multi-band-OFDM wirelesscommunications system made from a multi-band-OFDM wirelesscommunications system whose frequency allocation may have been shown inFIG. 10.

With each transmission band being made by binding three smallertransmission bands (and using the frequency allocation chart 1000 as adiscussion reference), each transmission band may have a bandwidth of1584 MHz and when using OFDM with no coding and no spreading, a maximumbit rate of 1920 Mbps may be possible. Once again, the transmissionbands may be partitioned into groups of three, such as group #1 1105that can be made up of transmission bands #1, #2, and #3. Note thatsince each transmission band is made up of three smaller transmissionbands, the total number of transmission bands available in themulti-band-OFDM wireless communications system is smaller than the totalnumber of transmission bands available in the multi-band-OFDM wirelesscommunications system shown in FIG. 10. Furthermore, FIG. 11 displaysone possible spectrum allocation and that there may be other possiblespectrum allocations.

Note that with such large transmission bands (in terms of bandwidth) andcorrespondingly, a small number of transmission bands, it may be morelikely to use FDM-OFDM rather than TFI-OFDM. However, it may be possibleto create a TFI-OFDM wireless communications system using groups of twobands, wherein group #1 1205 may include transmission bands #1 and #2and group #2 1210 may include transmission bands #3 and #4. Then, TFISsequences of length four may be used. For example, group #1 1205 may useTFIS sequences [1 1 2 2] and [1 2 1 2] and group #2 1210 may use TFISsequences of [3 3 4 4] and [3 4 3 4]. Alternatively, it can be possibleto mix operating modes, wherein some of the transmission bands may makeuse of FDM-OFDM while others use TFI-OFDM. The operating mode can beprovided to the receivers during the configuration of the transmissionbands, such as prior to commencement of transmissions or during startup.

With reference now to FIG. 13, there is shown a diagram illustrating afrequency allocation chart 1300 for a multi-band-OFDM wirelesscommunications system, wherein some transmission bands have been bondedand some have not been bonded, according to a preferred embodiment ofthe present invention. FIGS. 10, 11, and 12 displayed frequencyallocation charts 1000, 1100, and 1200 for wireless communicationssystems wherein the transmission bands are homogeneous in nature, i.e.,each transmission band is equal in size to every other transmission bandin the wireless communications system. However, depending upon theavailable spectrum, the number of transmission bands, the individualdata rate and range requirements of transmitters, and so forth, thetransmission bands may vary in size.

The frequency allocation chart 1300 displays a spectrum allocation for amulti-band-OFDM wireless communications wherein the transmission bandscan vary in bandwidth. For example, transmission bands in group #1 1305,such as transmission band #1 1307, can be constructed by bonding twotransmission bands together, while transmission bands in group #2 1310,such as transmission band #4 1312 may have the bandwidth of a singletransmission band. Note that the spectrum allocation shown in FIG. 13may be one of many different possible configurations, and that thefrequency allocation chart 1300 should not be construed as limiting thespirit of the present invention.

The spectrum allocation may be static or dynamic in nature. For a staticspectrum allocation, the transmission bands may be allocated during aninitial power-on sequence and may be set to provide a specific data rateor range performance requirement. The performance requirement may alsospecify a certain performance level under the presence of a specifiedamount of interference. According to a preferred embodiment of thepresent invention, the data rate and/or range performance requirementmay be programmed into a controller that may be responsible forcoordinating communications in a multi-band-OFDM wireless communicationssystem during the configuration of the controller. The performancerequirement may also be in hardware, software, or in a firmware upgrade.Furthermore, the performance requirement may be specified by aregulatory body (such as the Federal Communications Commission in theUnited States), an application using the multi-band-OFDM wirelesscommunications system, a compliance and interoperability body (such asWiMedia, a compliance body to ensure interoperability for personal-areawireless devices or similarly, the Multi-band OFDM Alliance), or amanufacturer of the multi-band-OFDM communications systems.

Alternatively, during normal operations, the controller may be placedinto a special configuration mode wherein the data rate and/or rangeperformance requirements may be specified. Once the data rate and/orrange performance requirements may be specified, the multi-band-OFDMwireless communications system may be reset in order to reconfigure thetransmission bands. Alternatively, the spectrum allocation may bedynamic in nature, wherein the transmission bands can change based uponthe needs of communicating devices in the multi-band-OFDM wirelesscommunications network.

With reference now to FIG. 14, there is shown a flow diagramillustrating an algorithm 1400 for use in configuring transmission bandsfor a multi-band-OFDM wireless communications system, according to apreferred embodiment of the present invention. According to a preferredembodiment of the present invention, the algorithm 1400 may execute on aprocessing element, a controller, a general purpose central processingunit, a custom design application specific integrated circuit, or soforth, of a controller that may be responsible for coordinatingcommunications in the multi-band-OFDM wireless communications system.The controller can often be referred to as a piconet coordinator or anaccess point. The controller can execute the algorithm 1400 during apower-up sequence, after a reboot, or after the execution of a specificoperation to initialize the reconfiguration of the transmission bands.

The controller can begin by retrieving performance requirements for themulti-band-OFDM wireless communications system from memory (block 1405).According to a preferred embodiment of the present invention, theperformance requirements may specify a desired data rate and/or rangeperformance requirements. Based upon the performance requirements, thecontroller can determine the size (bandwidth) of the transmission bands(block 1410). If the performance requirements are low, then the size ofthe transmission bands can be low, while if the performance requirementsare high, then the size of the transmission bands can be high. Afterdetermining the size of the transmission bands, which can also determinethe number and center frequencies of the transmission bands, thecontroller can configure the transmission bands (block 1415). Afterconfiguration (block 1415), the controller can initialize thecommunications (block 1420). Initialization may entail the controllerproviding the configuration of the transmission bands to thetransmitters and receivers in the multi-band-OFDM wirelesscommunications system. After initialization, the controller can completethe execution of the algorithm 1400.

With reference now to FIG. 15, there is shown a flow diagramillustrating an algorithm 1500 for use in bonding transmission bands fora multi-band-OFDM wireless communications system, according to apreferred embodiment of the present invention. According to a preferredembodiment of the present invention, the algorithm 1500 may execute on aprocessing element, a controller, a general purpose central processingunit, a custom design application specific integrated circuit, or soforth, of a controller that may be responsible for coordinatingcommunications in the multi-band-OFDM wireless communications system.The controller can execute the algorithm 1400 when there is a need foradditional data rate or range than what is currently available.

A dynamic spectrum allocation algorithm can offer the ability to changethe transmission bands based upon the demands of the communicatingdevices (transmitters and receivers) in the multi-band-OFDM wirelesscommunications network. This ability can help improve the ability of themulti-band-OFDM wireless communications network to meet the performancerequirements of the communications devices. According to a preferredembodiment of the present invention, when a communicating device needsto change its performance requirements (i.e., data rate and/or rangeperformance requirements), the communicating device may transmit therequest to the controller.

The controller can begin the execution of the algorithm 1500 when itreceives a request(s) from communicating devices for more data rateand/or range performance (block 1505). If no requests are received or ifthe request can be met without channel bonding (blocks 1505 and 1510),then the algorithm 1500 can terminate. The controller can then determinethe needed bandwidth to support the requested data rate and/or rangeperformance (block 1515). Based on the needed and available bandwidth,the controller can bond together transmission bands and allocate them tothe communicating device making the request (block 1520). Note that notshown may be additional operations that may be taken by the controllerto free sufficient bandwidth in order to bond adjacent transmissionbands. For example, the controller may need to move allocatedtransmission bands in order to have a sufficient number of adjacenttransmission bands to bond together. This can be referred to ascompacting the transmission spectrum. Compacting algorithms areconsidered to be well understood by those of ordinary skill in the artof the present invention and will not be discussed herein.

After allocating the transmission bands to the communicating device, thecontroller can monitor the communications to determine if the desireddata rate and/or range performance is met (block 1525). If the desireddata rate and/or range performance is met, then the algorithm 1500 canterminate. If the desired data rate and/or range performance is not met,then the controller can check if there is additional bandwidth available(block 1530). Once again, the controller may be required to perform acompaction of the transmission spectrum to find additional bandwidth. Ifthere is no additional bandwidth, then the desired data rate and/orrange performance cannot be met (block 1535) and the algorithm canterminate. If there is additional bandwidth, then the controller canbond additional transmission bands together (block 1540) and then returnto block 1525 where it can monitor if the desired data rate and/or rangeperformance requirements are being met.

Note that a performance requirement request from communicatingrequirement may typically be a request for additional transmissionbandwidth to support a higher data rate or a greater transmission range.However, communicating equipment may also release allocated bandwidthvia a performance request. For example, after the communicatingequipment has completed transmitting a large file, the communicatingequipment can release the transmission bandwidth by requesting a smaller(or no) transmission bandwidth and then releasing the large transmissionbandwidth previously allocated.

Alternatively, the communicating devices may be used to perform theperformance monitoring. Since the communicating devices are using thetransmission bands, they may be able to monitor the data rates and rangeperformance more readily than the controller. The communicating devicescan then provide to the controller a request for additional bandwidth ifthe data rate and/or range performance are not being met.

With reference now to FIG. 16, there is shown a diagram illustrating awireless communications system 1600 containing both legacy and enhancedcommunications devices and a piconet coordinator, according to apreferred embodiment of the present invention. As discussed previously,a piconet coordinator 1605 for an enhanced multi-band-OFDM wirelesscommunications system may be able to operate with both enhancedcommunications devices 1610 and legacy communications devices 1615. Ifthe piconet coordinator 1605 and the enhanced communications devices1610 uses an enhanced preamble, such as those shown in FIGS. 6 and 7,and the legacy communications devices 1615 uses a legacy preamble, thenthe enhanced communications devices 1610 can make use of the additionaltransmissions bands in addition to sharing the legacy transmissionsbands with the legacy communications devices 1615. It may be possible toprovide a measure of load balancing, wherein if there is a large numberof legacy communications devices 1615 making use of the legacytransmissions bands, the enhanced communications devices 1610 mayexclusively use the enhanced transmissions bands to help alleviatecongestion of the legacy transmissions bands. Note that thetransmissions between the enhanced communications devices 1610 and thepiconet coordinator 1605 may take place over bonded transmission bands.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1-41. (canceled)
 42. A method of communication in a wireless networkcomprising one or more simultaneously operating pico networks, themethod comprising: dividing the UWB spectrum into a plurality offrequency bands; forming one or more band groups including one or morefrequency bands from the plurality of frequency bands; assigning atleast one band group to each one of the pico networks; assigning atleast one time frequency code to symbols associated with each one of thepico networks on a transmission-by-transmission basis, wherein the timefrequency code represents one of a single frequency band and apre-defined sequencing across all the frequency bands within theassigned band group; and communicating data within each one of the piconetworks using the assigned band groups according to the time frequencycode.
 43. The method of claim 42, wherein each frequency band is 528 MHzwide.
 44. The method of claim 43, wherein a center frequency of eachfrequency band is given by:FC(N)=3432+528*(N−1) MHz, wherein FC(N) is the center frequency of bandN.
 45. The method of claim 42, further comprising: assigning a preambleto one or more of the pico networks.
 46. The method of claim 44, whereinthe UWB spectrum includes at most twelve frequency bands.
 47. The methodof claim 46, wherein the UWB spectrum comprises at least-three bandgroups each including three frequency bands.
 48. The method of claim 46,wherein the UWB spectrum comprises four band groups each including threefrequency bands.
 49. The method of claim 8, wherein at least one of theband groups is placed above 4752 MHz in the UWB spectrum.
 50. A systemfor channelization of a spectrum in a wireless network comprising one ormore simultaneously operating pico networks, the system comprising: afrequency-synthesized oscillator configured to generate a signal insteps of 528 MHz beginning at center frequency of 3432 MHz and ending atcenter frequency of 9240 MHz; and a time frequency code generatorcoupled to the frequency-synthesized oscillator and configured to assigntime-frequency codes to successive transmissions of a pico network suchthat the successive transmissions are transmitted in all frequency bandsof a band group assigned to the pico network.
 51. A system according toclaim 50, wherein the spectrum comprises at least two band groups eachincluding at least three frequency bands, and at least two band groupseach including at least four frequency bands.
 52. A system according toclaim 50, wherein the spectrum comprises at least three band groups eachincluding three frequency bands.
 53. A system according to claim 52,wherein the spectrum comprises four band groups each including threefrequency bands.
 54. A system according to claim 52, wherein at leastone of the band groups is placed above 4752 MHz in the spectrum.